A281303 Numbers k such that (10^k + 77)/3 is prime.

1, 2, 3, 4, 5, 8, 16, 20, 56, 58, 75, 109, 124, 217, 221, 368, 439, 595, 1309, 6986, 11600, 20855, 29327, 34305, 42145, 44056, 52667, 75707, 79067, 81848, 119836, 164284, 176584

Offset

1,2

Comments

For k>1, numbers such that k-2 occurrences of the digit 3 followed by the digits 59 is prime (see Example section).

a(34) > 2*10^5.

Links

Table of n, a(n) for n=1..33.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 3w59.

Example

3 is in this sequence because (10^3 + 77)/3 = 359 is prime.
Initial terms and primes associated:
a(1) = 1, 29;
a(2) = 2, 59;
a(3) = 3, 359;
a(4) = 4, 3359;
a(5) = 5, 33359; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(10^# + 77)/3] &]

Crossrefs

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A112479 A333264 A247461 * A264011 A337280 A081711

Adjacent sequences: A281300 A281301 A281302 * A281304 A281305 A281306

Keyword

nonn,more,hard

Author

Robert Price, Jan 21 2017

Extensions

a(31)-a(33) from Robert Price, Jan 18 2018

Status

approved